1. Field of the Invention
This invention relates to the field of mechanical refrigeration systems and methods wherein the refrigerant is alternately vaporized and condensed. The mechanical compressor employed in the system may be rotary, rotary vane, piston, etc.
2. Description of Prior Art
There is a major need, for example in automobile air conditioners, the air conditioners of small aircraft, etc., for a refrigeration system which can be extremely small and light in weight, and is efficient and capable of operating well in a hot environment (for example, under the hood of an automobile). To achieve large amounts of cooling with a small and light refrigeration system, it is necessary that the compressor be driven at a very high speed. Resulting frictional effects, in addition to the heat generated by compressing the refrigerant vapor, create a great deal of heating -- with consequent problems relating to lubrication, carbon formation, etc. Heating is also exacerbated by the hot environment in which the system may operate.
Heating of the compressor causes (1) lowering of the volume of vapor which the compressor will handle at a given speed, (2) an excessively high superheat in the vapor, (3) a lowering of efficiency, and (4) the problems relative to lubrication and carbon formation. It follows that cooling of the compressor is critically important, but it must be done effectively, economically and in such a way as not to affect adversely the operation or size of the compressor or of other portions of the system. It is highly important that effective cooling occur in regions where heating is the worst. It is also highly important that effective cooling occur in the absence of expensive oil cooling means, since such means add greatly to the bulk and expense of the system.
There are large numbers of patents directed to the problem of cooling the compressor in a mechanical refrigeration system, or to associated problems. These include: U.S. Pat. Nos. 1,893,171; 2,178,425; 2,306,632; 2,470,655; 2,510,887; 3,105,633; 3,109,297, 3,111,820; 3,210,958; 3,250,460; 3,291,385; 3,379,033; 3,402,571; and 3,423,013. Most of the listed patents relate to the direct injection of liquid refrigerant into the compression chamber, in order that the liquid will expand in such chamber and therefore create a cooling action. However, the cooling action is not as continuous or effective as is that of the present invention. Furthermore, certain common refrigerants create, when in liquid form, an adverse effect relative to the lubricant present in the compression chamber.
U.S. Pat. No. 2,510,887 relates to a compressor in which there is no injection of liquid refrigerant into the compression chamber, the liquid refrigerant instead flowing around the compressor wall in heat-exchange relationship to the compression chamber and the head. Relative to the system of such U.S. Pat. No. 2,510,887, there is believed to be no substantial amount of vaporization of liquid in the heat-exchange circuit, nor is there effective heat transfer with certain of the hottest parts of the compressor, which means that the degree of cooling of the compressor is low. Furthermore, the refrigerant is educted into the compressor outlet, at elevated temperature, which tends to produce an adverse effect upon the system.
Another patent, U.S. Pat. No. 3,379,033, is such as to make workers skilled in the art believe that an oil-cooling means is required. Vaporizing refrigerant is employed to cool the oil in an oil-cooling circuit, at a location outside the compressor. A mixture of vaporous and liquid refrigerant is discharged from the external oil cooler and then further vaporized in an open annular chamber surrounding the cylinder wall. However, the characteristics of the open annular chamber are such that there is insufficient heat transfer with the hottest compressor regions. Thus, the U.S. Pat. No. 3,379,033 not only teaches a complex, large-size cooling means but one wherein compressor cooling is relative inefficient and ineffective. Additionally, the refrigerant is passed from such open chamber directly into the compressor suction line, thereby decreasing compressor efficiency under load condition.
Both of the U.S. Pat. Nos. 2,510,887 and 3,379,033 teach means for automatically regulating the amount of cooling action. Such means are, however, deficient in that (a) they are not quickly responsive to compressor temperature and/or (b) they do not use pressure of the cooling refrigerant as a means to control compressor temperature.